Ziprasidone, of formula (I)

is an antipsychotic drug known from U.S. Pat. No. 4,831,031. The process for the preparation of ziprasidone disclosed in U.S. Pat. No. 4,831,031 comprises the formation of a compound (II) by reduction of a compound (III) and subsequent reaction with a compound (IV), according to the following scheme:

The reduction of a compound (III) to form a compound (II) is carried out by reaction with trifluoroacetic acid and triethylsilane, which are very expensive, thus remarkably affecting the product cost. Chloroketone (III) is an eye irritant and its presence, even in traces, as an impurity in intermediate (II) and in the final product, is a problem for operators. Moreover, said impurity reacts with a compound (IV) to form a further impurity (A), 5-(2-(4-benzo[d]isothiazol-3-yl)piperazin-1-yl)acetyl)-6-chloro-1,3-dihydro-2H-indol-2-one, which is present in the final product and is difficult to remove.

The drawbacks of the process according to U.S. Pat. No. 4,831,031 are thus evident. There is therefore the need for an improved process for the preparation of zipresidone which is less expensive and free from the drawbacks of the known methods.